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[o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Log in</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Pages for logged out editors <a href="/wiki/Help:Introduction" aria-label="Learn more about editing"><span>learn more</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Special:MyContributions" title="A list of edits made from this IP address [y]" accesskey="y"><span>Contributions</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Special:MyTalk" title="Discussion about edits from this IP address [n]" accesskey="n"><span>Talk</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <h1 id="firstHeading" class="firstHeading mw-first-heading">View source for Flat engine</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="This article exist only in this language. Add the article for other languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-0" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">Add languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> <div class="after-portlet after-portlet-lang"><span class="uls-after-portlet-link"></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Flat_engine" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:Flat_engine" rel="discussion" title="Discuss improvements to the content page [t]" accesskey="t"><span>Talk</span></a></li> </ul> </div> </div> <div id="vector-variants-dropdown" class="vector-dropdown emptyPortlet" > <input type="checkbox" id="vector-variants-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-variants-dropdown" class="vector-dropdown-checkbox " aria-label="Change language variant" > <label id="vector-variants-dropdown-label" for="vector-variants-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span 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Flat engines are also known as '''horizontally opposed engines''', however this is distinct from the less common [[opposed-piston engine]] design, whereby each cylinder has two pistons sharing a central combustion chamber. The most common configuration of flat engines is the [[#Boxer configuration|boxer engine]] configuration, in which the pistons of each opposed pair of cylinders move inwards and outwards at the same time. The other configuration is effectively a [[V engine]] with a 180-degree angle between the cylinder banks: in this configuration each pair of cylinders shares a single crankpin, so that as one piston moves inward, the other moves outward. The first flat engine (Benz Contramotor) was built in 1897 by [[Karl Benz]]. Flat engines have been used in aviation, motorcycle and automobile applications. They are now less common in cars than [[straight engine]]s (for engines with fewer than six cylinders) and [[V engine]]s (for engines with six or more cylinders). Flat engines are more common in aircraft, where straight engines are a rarity and V engines have almost vanished except in historical aircraft. They have even replaced [[radial engine]]s in many smaller installations. == Design == {{More citations needed section|date=February 2021}} [[File:Moteurs à Plat - V à 180° vs. Boxer.png|thumb|Difference between two flat 6 cylinder engines: 180° V on the left, boxer on the right]] The advantages of flat engines are a short length, low [[centre of mass]] and suitability for [[Air-cooled engine|air cooling]] (due to the well-exposed, large-surface-area cylinders and cylinder heads, and their short length). Compared with the more common [[straight engine]]s, flat engines have better [[primary balance]] (resulting in less vibration);<ref>{{cite web |title=The Physics of: Engine Cylinder-Bank Angles |url=https://www.caranddriver.com/features/a15126436/the-physics-of-engine-cylinder-bank-angles-feature/ |website=www.caranddriver.com |access-date=2019-10-18 |date=2019-10-14}}</ref> however, the disadvantages are increased width and the need to have two cylinder heads. Compared with [[V engine]]s – the most common layout for engines with six cylinders or more – flat engines again have a lower centre of mass, and, for six-cylinders, better primary balance; the disadvantage is again their being wider.<ref name="why-subaru">{{cite web |url=https://www.subaru.com.au/why-subaru/performance |title=Subaru Car Performance |publisher=Subaru |location=Australia |access-date=2020-07-01}}</ref> The most common usages of flat engines are: * [[Flat-twin engine]]s are mostly used in motorcycles. Occasionally they have been used in light cars, aircraft and industrial applications, mostly up until the 1960s. * [[Flat-four engine]]s are mostly used in cars (most notably in the earlier [[Volkswagen]] [[Volkswagen Beetle|Types 1]] to [[Volkswagen Type 4|4]], and by [[Subaru]]<ref name="why-subaru"/> in most of their models), and have occasionally been used in motorcycles. Their most common use is in smaller single-engine [[general aviation|general-aviation]] aircraft, for which they are still manufactured and used to this day. * [[Flat-six engine]]s are mostly used in aircraft and cars (particularly by the [[Porsche]] 911 sports car), and have occasionally been used in motorcycles. * [[Flat-eight engine]]s have been used in several racing cars, mostly by Porsche in the 1960s. * [[Flat-ten engine]]s are not known to have reached production. A prototype road car engine was built by [[Chevrolet]] in the 1960s. * [[Flat-twelve engine]]s have been used in various racing cars, notably the [[Porsche 917K]], during the 1960s and 1970s, and in [[Ferrari]] road cars from 1973 to 1996. * [[Flat-sixteen engine]]s are not known to have reached production. Prototype racing car engines were built by [[Coventry Climax|Coventry]] and Porsche in the 1960s and 1970s. === Boxer configuration {{anchor|Boxer engine}}=== [[File:R68-opposed-cylinders.jpg|thumb|right|1954 [[BMW R68]] flat-twin boxer engine]] Most flat engines use a "boxer" configuration, where each pair of opposing pistons move inwards and outwards at the same time, somewhat like boxing competitors punching their gloves together before a fight.<ref name=Bonk>{{cite web |last=Bonk |first=Aaron |title=How Boxer Engines Work |url=http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/ |work=Super Street Magazine |publisher=Source Interlink Media |access-date=2013-12-21 |date=2013-02-07 |archive-date=27 February 2014 |archive-url=https://web.archive.org/web/20140227052947/http://www.superstreetonline.com/techarticles/sstp_1301_how_boxer_engines_work/ |url-status=dead }}</ref> Boxer engines have low vibration, being they are the only common configuration that has no unbalanced forces, regardless of the number of pairs of cylinders. Boxer engines therefore do not require either a [[balance shaft]]<ref name=Hanlon/> or counterweights on the [[crankshaft]] to balance the weight of the reciprocating parts. However, a [[Couple (mechanics)#Applications|rocking couple]] is present, since each cylinder is slightly offset from the other member of its pair due to the distance between the [[crankpin]]s along the crankshaft.<ref name=Bonk/> === 180-degree V engine === An alternative configuration for flat engines is as a 180-degree [[V engine]], which has been used on most twelve-cylinder flat engines. In this configuration, each pair of pistons shares a [[crankpin]], this being simpler than the boxer configuration, where each piston has its own separate crankpin. ==Aviation use== [[File:Puch Flugmotor Patent AT 48877 1909-11-08.png|thumb|right|Twin-boxer of [[Johann Puch]], Patent AT 48877 (1909)]] [[File:Riedelanlasser.jpg|thumb|right|World War II-era Riedel starter motor]] In 1902, the Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine. Amongst the first commercially-produced aircraft to use a flat engine was the 1909 [[Santos-Dumont Demoiselle]] range of aeroplanes, which was powered by boxer-twin engines.{{Citation needed|date=March 2021}} Several boxer-four engines have been produced specifically for light aircraft. A number of manufacturers produced boxer-six aircraft engines during the 1930s and 1940s.{{Citation needed|date=March 2021}} During World War II, a boxer-twin engine called the "Riedel starter" was used as a starter motor/mechanical [[Auxiliary power unit#As mechanical "startup" APUs for jet engines|APU]] for the early German jet engines, such as the [[Junkers Jumo 004]] and [[BMW 003]]. Designed by [[Norbert Riedel]], these engines have a very [[Stroke ratio#Oversquare or short-stroke engine|oversquare]] stroke ratio of 2:1 so that they could fit within the intake diverter, directly forward of the turbine compressor.{{Citation needed|date=March 2021}} {{clear right}} ==Motorcycle use== Flat engines offer several advantages for motorcycles including a low [[centre of mass]], low vibration, suitability for shaft drive, and equal cooling of the cylinders (for air-cooled engines).<ref name=English /><ref name=Szymezak1>{{cite web |last=Szymezak |first=Pascal |title=Début de la légende |url=http://fgwcf.org/rever/debut_legende.asp |work=La saga GoldWing |publisher=Fédération des GoldWing Club de France |language=fr |access-date=2013-12-20 |url-status=dead |archive-url=https://web.archive.org/web/20131219232421/http://fgwcf.org/rever/debut_legende.asp |archive-date=2013-12-19 }}</ref> The most common design of flat engine for motorcycles is the boxer-twin, beginning with the 1905 Fée flat-twin engine, manufactured by the Light Motors Company, which was the first production motorcycle engine.<ref name=TMCfuture>{{cite journal |date=1916-10-05 |title=The engine of the future |page=283 |journal=[[The Motor Cycle (magazine)|The Motor Cycle]] |publisher=Iliffe & Sons Ltd.}}</ref> [[BMW Motorrad]] have a long history of boxer-twin motorcycles, beginning in 1923 with the [[BMW R32]]<ref name=English /> Several motorcycles have been produced with flat-four engines, such as the 1938–1939 [[Zündapp|Zündapp K800]] and the 1974–1987 [[Honda Gold Wing]]. In 1987, the Honda Gold Wing engine was upsized to a flat-six design.<ref>{{Cite web |title=Overview – GL1800 Gold Wing – Touring – Range – Motorcycles – Honda |url=https://www.honda.co.uk/motorcycles/range/touring/gl1800-gold-wing/overview.html |access-date=2024-10-09 |website=Honda UK}}</ref> ==Automotive use== {{multiple image | align = right | direction = vertical | width = 220 | image1 = Diesel Engine Type DS140 2C Hino.jpg | caption1 = 1969 [[Hino Motors]] DS140 boxer-twelve diesel engine | image2 = ChassisT11.JPG | caption2 = 1923-1927 [[Tatra 11]] chassis and engine— front-mounted flat-twin engine with rear-wheel drive }} When used in cars, advantages of flat engines are a low [[centre of mass]] (which improves the handling of the car),<ref name=Hanlon>{{cite news |last=Hanlon |first=Mike |title=The world's first horizontally-opposed turbo diesel engine |url=http://www.gizmag.com/go/6800/ |work=Gizmag |date=2001-02-07 |access-date=2013-12-20}}</ref> short length, low vibration and suitability for air cooling (due to the well exposed, large surface area, cylinder heads and short length).{{Sfn|Nunney|1988|pp=12–13}} However the larger width of flat engines (compared with the more common inline and V layouts) is a drawback, particularly when the engine is located between the steered wheels.{{Citation needed|date=March 2021}} Flat engines were used by various automobile manufacturers – mostly with a boxer-four design – up until the late 1990s. Since then, only Porsche and Subaru have remained as significant manufacturers of flat engines.{{Citation needed|date=March 2021}} === Drivetrain layout === {{More citations needed section|date=February 2021}} Due to the short length of flat engines, locating a flat engine outside of the car's [[wheelbase]] results in minimal overhang.<ref>{{Cite book |last= Nunney|first= M. J.|title= Light and Heavy Vehicle Technology|publisher= Heinemann Professional Publishing|location= Oxford, UK|year= 1988|isbn= 0-434-91473-8|url= {{Google books|-vj8BAAAQBAJ|Light and Heavy Vehicle Technology|page=12|plainurl=yes}}|access-date=2015-05-08|page= 12}}</ref> Therefore, many cars with flat engines have used a [[rear-engine, rear-wheel-drive layout]]. Examples include the flat-twin [[BMW 600]] (1957–1959) and [[BMW 700]] (1959–1965); the flat-four [[Tatra 97]] (1936–1939), [[Volkswagen Beetle]] (1938–2003) and [[Porsche 356]] (1948–1965); and the flat-six [[Chevrolet Corvair]] (1959–1969), [[Porsche 911]] (1963-present), and [[Tucker 48]] (1947–1948). The opposite layout, [[front-engine, front-wheel-drive layout|front-engine front-wheel drive]], was also common for cars with flat engines. Examples include the [[Citroën 2CV]] (1948–1990), [[Panhard Dyna X]] (1948–1954), [[Lancia Flavia]] (1961–1970), [[Citroën GS]] (1970–1986), [[Alfa Romeo Alfasud]] (1971–1989) and [[Subaru Leone]] (1971–1994). Subaru have been producing cars with a [[front-engine, four-wheel-drive layout]] powered by flat engines (mostly boxer-four engines) since 1971. Examples include the [[Subaru Leone]] (1971–1994), [[Subaru Legacy]] (1989-present) and [[Subaru Impreza]] (1992–present). The front half-shafts come out of a front differential that is part of the gearbox. A rear driveshaft connects the gearbox to the rear half-shafts. The traditional [[front-engine, rear-wheel-drive layout]] is relatively uncommon for cars with flat engines, however some examples include the [[Toyota 86|Toyota 86 / Subaru BRZ]] (2012–present), [[Jowett Javelin]] (1947–1953), [[Glas Isar]] (1958–1965) and the [[Tatra 11]] (1923–1927). ===History=== {{More citations needed section|date=February 2021}} {{multiple image | align = right | direction = vertical | width = 220 | image1 = Volkswagen motor cut 1945.JPG | caption1 = [[Volkswagen air-cooled engine|Volkswagen air-cooled]] boxer-four engine | image2 = Subaru BRZ engine (20413082204).jpg | caption2 = 2012-present [[Subaru FA engine|Subaru FA20]] boxer-four engine }} The first flat engine was produced in 1897 by German engineer [[Karl Benz]].<ref name=English>{{cite news |last=English |first=Bob |title=The engine that Benz built still survives |url=https://www.theglobeandmail.com/globe-drive/car-life/classic-cars/the-engine-that-benz-built-still-survives/article4317376/ |access-date=2013-12-19 |newspaper=The Globe and Mail |location=Canada |date=2010-04-29 |archive-date=20 December 2013 |archive-url=https://web.archive.org/web/20131220085552/http://www.theglobeandmail.com/globe-drive/car-life/classic-cars/the-engine-that-benz-built-still-survives/article4317376/ |url-status=dead }}</ref><ref>{{cite web|last=Hodzic |first=Muamer |title=Mercedes Heritage: Four-cylinder engines from Mercedes-Benz |url=http://www.benzinsider.com/2008/03/mercedes-heritage-four-cylinder-engines-from-mercedes-benz/ |work=Blog |publisher=BenzInsider |access-date=2013-12-20 |date=2008-03-27}}</ref> Called the ''kontra'' engine, it was a boxer-twin design. Early uses of flat engines in cars include the 1900 [[Lanchester Motor Company|Lanchester 8&nbsp;hp Phaeton]] boxer-twin, the 1901 [[Wilson-Pilcher]] boxer-four,<ref name="Automotor">{{cite journal |title=The Wilson-Pilcher Petrol Cars |journal=The Automotor Journal |date=1904-04-16}}</ref> the 1904 Wilson-Pilcher ''18/24 HP'' boxer-six and the 1903 [[Ford Model A (1903–1904)|Ford Model A]], the 1904 [[Ford Model C]] and the 1905 [[Ford Model F]].<ref name="Kimes">{{cite book|last=Kimes |first=Beverly |title=Standard Catalog of American Cars 1805-1942 |year=1996 |publisher=Krause Publications |isbn=0-87341-428-4 |page=572 }}</ref> In 1938, the [[Volkswagen Beetle]] (then called the "KdF-Wagen") was released with a rear-mounted flat-four engine. This [[Volkswagen air-cooled engine]] was produced for many years and also used in the [[Volkswagen Type 2]] (Transporter, Kombi or Microbus), the [[Volkswagen Karmann Ghia]] sports car and the [[Volkswagen Type 3]] compact car. A water-cooled version, known as the [[Wasserboxer]], was introduced in 1982 and eventually replaced the air-cooled versions. The majority of sports cars throughout Porsche's history are powered by flat engines, beginning with its first car; the 1948-1965 [[Porsche 356]] used an air-cooled boxer-four engine. Also using boxer-four engines were the 1969-1976 [[Porsche 914]], the 1965-1969 [[Porsche 912]] and the 2016-present [[Porsche 982|Porsche Boxster/Cayman (982)]]. The [[Porsche 911 (classic)|Porsche 911]] has exclusively used boxer-six engines from its introduction in 1964 until the present. In 1997, the Porsche 911 switched from being air-cooled to water-cooled. [[Porsche flat-eight engines]] were used in various racing cars throughout the 1960s, such as the 1962 [[Porsche 804]] Formula One car and the 1968-1971 [[Porsche 908]] sports car. A flat-twelve engine was also produced by Porsche for the 1969-1973 [[Porsche 917]] sports car. [[Chevrolet]] used a horizontally opposed air-cooled 6 cylinder engine in its [[Chevrolet Corvair|Corvair]] line during its entire production run from 1960 to 1969 in various applications and power ratings, including one of the first uses of a turbocharger in a mass-produced automobile. The [[Subaru EA engine]] was introduced in 1966 and began [[Subaru]]'s line of boxer-four engines that remain in production to this day.<ref>{{cite web |title=Distinct Engineering Mounted into the Subaru 1000 |url=http://subaru-philosophy.com/post/29112851147/distinct-engineering-mounted-into-the-subaru-1000 |work=SUBARU Philosophy |publisher=Fuji Heavy Industries Ltd |access-date=2013-12-20 |date=2012-08-10 |quote=Source: 'Subaru' magazine – Subaru 1000 extra edition (issued 1966-05-20) |archive-date=21 December 2013 |archive-url=https://web.archive.org/web/20131221053109/http://subaru-philosophy.com/post/29112851147/distinct-engineering-mounted-into-the-subaru-1000 |url-status=dead }}</ref> Most of Subaru's models are powered by a boxer-four engine in either naturally aspirated or turbocharged form. A print ad for the 1973 [[Subaru GL]] coupe referred to the engine as "quadrozontal".<ref>{{cite web|url=http://www.scoobyblog.com/2007-01-04/vintage-subaru-ad-1973-the-subaru-gl-coupe |title=» Vintage Subaru Ad (1973 The Subaru GL Coupe) |publisher=Scoobyblog.com |access-date=2010-09-18}}</ref> The company also produced boxer-six engines from 1988 to 1996 and 2001–2019.<ref>{{cite web |title=Flat-6 Club: 1993 Subaru Impreza w/ Legacy 6-Cyl |url=http://www.dailyturismo.com/2018/06/flat-6-club-1993-subaru-impreza-w.html |website=www.dailyturismo.com |date=12 June 2018 |access-date=21 September 2019 |archive-date=21 September 2019 |archive-url=https://web.archive.org/web/20190921022942/http://www.dailyturismo.com/2018/06/flat-6-club-1993-subaru-impreza-w.html |url-status=dead }}</ref> In 2008, the [[List of Subaru engines#Subaru EE engine (diesel)|Subaru EE]] engine became the world's first passenger car diesel boxer engine. This engine is a turbocharged boxer-four with common rail fuel injection.<ref name=Hanlon /><ref>{{cite web |title=Greencarcongress |work=Legacy Diesel Announcement |url=http://www.greencarcongress.com/2008/01/subarus-first-b.html |access-date=2008-01-23}}</ref><ref>{{cite web |last=Harwood |first=Allyson |title=2008 Subaru Turbodiesel Boxer - First Drive |url=http://www.motortrend.com/roadtests/sedans/112_0801_subaru_boxer_turbodiesel_first_drive/viewall.html |work=MotorTrend Magazine |publisher=Source Interlink Media |access-date=2013-12-20 |date=January 2008}}</ref><ref>{{cite web |title=A True Engineering Revolution |url=http://www.boxerdiesel.com/engineering/en/01.html |work=SUBARU BOXER DIESEL |publisher=Fuji Heavy Industries Ltd |access-date=2013-12-20 |archive-url=https://web.archive.org/web/20140301122607/http://boxerdiesel.com/engineering/en/01.html |archive-date=2014-03-01 |url-status=dead }}</ref> Ferrari used flat-twelve engines for various Formula One cars in the 1970s. A road car flat-twelve engine (using a 180-degree V12 configuration) was used for the 1973-1984 [[Ferrari Berlinetta Boxer]], 1984-1996 [[Ferrari Testarossa]] and their derivatives.<ref>{{cite web |title=Flat-12 engine |url=http://www.ferrari.com/English/GT_Sport%20Cars/RacingInnovation/Pages/Flat_12_engine.aspx |work=Ferrari.com |publisher=Ferrari S.p.A. |access-date=2013-12-21 |archive-url=https://web.archive.org/web/20131225102235/http://www.ferrari.com/English/GT_Sport%20Cars/RacingInnovation/Pages/Flat_12_engine.aspx |archive-date=2013-12-25}}</ref> Toyota uses the designation ''Toyota 4U-GSE'' for the boxer-four engine in the Toyota-badged versions of the [[Toyota 86|Toyota 86 / Subaru BRZ]] twins, although the engine is actually designed and built by Subaru as the [[Subaru FA engine#FA20|Subaru FA20]] engine.<ref name=Bonk /> ==See also== * [[H engine]] * [[V engine]] * [[W engine]] * [[X engine]] * [[Radial engine]] * [[History of the internal combustion engine]] ==References== 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